As is known in the art, hypodermic syringes include an elongate barrel having opposed proximal and distal ends with a chamber therebetween for receiving a fluid. A passageway extends through the distal end of the syringe barrel and communicates with the chamber. The distal end of the syringe barrel is connected to a piercing element, such as a needle cannula or a blunt cannula, for delivering fluid from the chamber and passageway. The proximal end of the syringe barrel receives a plunger rod and stopper assembly. Force applied to the plunger rod urges the stopper along the barrel to drive liquid from the chamber through the needle cannula.
Oftentimes, it is desired to deliver from the hypodermic syringe a number of discrete substances held within the chamber. These discrete substances normally must be held separate from one another until such time as delivery to the patient is desired. It is necessary, then, that the chamber defined between the proximal and distal ends of the elongate barrel be divided into a discrete number of chambers, each capable of holding a substance intended for delivery to a patient.
Bearing the foregoing in mind, it would be useful to construct a hypodermic syringe capable of simultaneously storing a medicament together with any components which are to be administered, with the ability to keep the medicament and the components separate until administration is desired. Medicaments storable in hypodermic syringes can be in liquid form or in dry form. It is often desirable to store medicaments in dry form since, depending on the type of medicament, it will display a longer shelf-life vis-a-vis the liquid form of the drug. As the skilled artisan will appreciate, one way to reduce a liquid drug to dry form is through a lyophilization process. In this process, liquid medicaments are subjected to a freeze-drying, or lyophilization, process, that reduces the liquid medicament to a dried powder or granular form. For purposes of simplicity, reference in this patent application to a drug in lyophilized form is intended to encompass any dry medicament, all of which require reconstitution prior to delivery.
Frequently, dry medicaments are located in a multi-chamber syringe barrel in the chamber located most adjacent the piercing element. In order to administer the medicament to a patient, a diluent is introduced into the chamber containing the dry medicament in order to reconstitute the drug into its liquid form. Thereafter, the reconstituted medicament can be administered from the same multi-chamber syringe which had stored the lyophilized medicament. It is also desirable to isolate the dry medicament from the ambient environment until such time as reconstitution and delivery is desired.
With the foregoing objectives in mind, U.S. Pat. No. 4,929,230 to Frederick W. Pfleger ("Pfleger '230"), whose disclosure is specifically incorporated by reference herein, describes a particular stopper construction useful for dividing the syringe barrel into a plurality of chambers and allowing separate liquid contents held by the syringe barrel to be sequentially administered to a patient. Making particular numerical reference to components disclosed by Pfleger '230, there is disclosed a free piston (or stopper) 33 including a hollowed chamber 48 facing the end wall 23 of the syringe barrel. Chamber 48 can be realized as a hollow circularly disposed about the central axis of stopper 33 (FIGS. 5, 6, 7) or, as shown in FIGS. 9, 10 or 11, it can assume a flattened, narrow configuration offset from the central axis of the stopper. Stopper 33 includes a closed end 34, which faces away from end wall 23 of the syringe barrel. Closed end 34 has a diameter less than the interior diameter of the syringe barrel. A peripheral sidewall 35 obliquely extends between closed end 34 of stopper 33 and a cylindrical peripheral sealing surface 36 in contact with the interior surface of the syringe barrel. Oblique sidewall 35 overlaps with a portion of hollowed chamber 48. It is stated at Col. 3, lines 15-17, that the oblique sidewall 35 has its large end generally cylindrical, as the sealing surface 36, for sealing engagement with the syringe barrel, and it is stated at Col. 3, lines 19-23, that external ribs 37 help prevent tipping of the piston as it moves in the syringe barrel. It is believed by the inventors herein that the oblique sidewall 35 is itself cylindrically formed around stopper 33 and, thus, extends about the entire circumference of the stopper. A force is generated by a proximal-most stopper 31 connected to plunger rod 30, stopper 33 will come to rest adjacent internal shoulder 25 of the syringe barrel. Continued motion by stopper 31 increases the fluid forces exerted upon oblique sidewall 35 to overcome the resilient material sealing forces inherent in stopper 33. Because of the presence of hollowed chamber 48, oblique sidewall 35 will collapse inwardly, allowing the fluid contents held proximally of closed end 34 to proceed in a distal direction for delivery through the needle cannula.
Pfleger '230 is not particularly suited to an application requiring the reconstitution of a dry drug before the sequential delivery of other components, such as flushes, retained by the syringe barrel. For instance, neither the teaching of Pfleger '230, nor the structure of Pfleger '230, is adapted to permit reconstitution of a medicament held in dry form in a chamber of the syringe barrel. Pfleger '230 is directed towards sequential delivery of liquid components but not to sequential delivery of a dry component.
Moreover, in certain prior art hypodermic syringes, a certain amount of liquid can remain in the syringe barrel after the stoppers are advanced the full length of the barrel during an injection process. There remains in most syringes a certain residual volume, no matter how small, which is trapped between the end of the stopper and the needle tip, which includes the volume of the needle cannula and the volume presented at the distal end of the syringe barrel. A quantity of the medication can also be trapped in the area around and between the sidewalls of the stopper and the interior of the syringe barrel. In the case of expensive medications and medications requiring extreme precision and delivery, this so-called "dead space" must be overcome by overfilling the barrel in order to ensure that the proper dose is delivered. The additional medication will be disposed of with the used syringe. The costs associated with the dead volume can accumulate substantially. It would be beneficial to prevent waste of medication trapped in the syringe barrel, for instance, as evidenced by Pfleger '230 between hollow end 48 of the stopper, internal shoulder 25 located at the extreme distal end of the syringe barrel, and outlet port 24 associated with the syringe barrel. A quantity of medication that can be held between these surfaces is seen, for instance, in FIG. 7 of Pfleger '230.
Accordingly, there is a need for a sequential stopper having bypass features to promote reconstitution of a dry drug held in a syringe barrel and which thereafter allows sequential injection of a series of disparate contents held in separate chambers in the syringe barrel, all of which results in reducing the amount of medicament trapped in the syringe barrel after delivery. Such a stopper is disclosed herein.